Microporous diaphragm



June 6, 1939- w. L. REINHARDT ET A1. 2,151,333

MICROPOROUS DIAPHRAGM faj Original Filed Nov. 20, 1933 PQM Mw ,f j/mf ATTORNEYS Patented 6, 1935 UNITED STATES l amas: MCRDPOROUS DIAPHBAGM PATENT OFFICE Willard L. Reinhardt, Shaker Heights, and Leland E. Wells, Cleveland Heights, Ohio, assignors to Willard `Storage Battery Company, Cleveland, Ohio, a corporation of West Virginia Original application November 20, 1933, Serial No. 698,860, now Patent No. 2,052,490, dated August 25, 1936. Divided and this application August 6, 1936, Serial No. 94,612

s clam.. (c1. 13s-14o) The principal object of lthe present invention is to provide diaphragms especially adapted for storage battery insulators or separators which have the desirable qualitiesand which are pracntically free from the undesirable characteristics l of the best separators' in use at the` present time. More particularly it is thepbject of this invention to provide a separator or diaphragm which has long life, which can be produced inexpensively, and which has the desired stiffness or rigidity, has low resistance, and'has a high degree of porosity but with the pores of microscopic size so as to be readily permeable to liquids, such as'the electrolyte of a storage battery, but not to solid particles of any appreciable size.

` The invention may be here briefly summarized ,25 as consisting in an improved diaphragm having the structural characteristics hereinafter described.

In the accompanying sheet of drawings wherein we have illustrated an embodiment of the invention which is highly successfulz Fig. 1 is a face view of a storage battery separator formed in accordance with our invention with portions broken away to show the interior sheet of fabric;

Fig. 2 is a transverse sectional view of the same; Fig. 3 is a face view of a separator modified as to the form of the ribs, a portion vonly of the sepa-V rator be'ng shown; and

v Fig. 4 is a transverse sectional view of the same.

Generally speaking, our improved diaphragm consists of a sheet or layer of porous material filled and coated with a suitable inert microporous material, such as microporous rubber, the coating and llng material being onlyy of sumcient thickness with respect to the sheet of porous material, which is preferably cotton fabric, to give the latter the required stiffness and rigidity,

and, ofcourse, to' provide the microscopic character toj'the porosity of the diaphragm as a whole.

Different kinds of porous material may be emv ployed, as, for example, cotton fabric or unwoven brous material, such as paper stock, but

preferably a thin sheet of woven cotton fabric with a fairly open weave is employed.

The microporous lling and coating material is preferably rubber, made either from natural latex `or artificial latex, preferably the former, in the 5 manner or in approximately the manner disclosed in United States Patent No. 1,745,657, granted February 4, 1930, to Hermann Beckmann. In following 4this procedure, latex` compounded with sulphur and possibly other ingredients, such as 10 and incidentally the serums, the retention of the 20 waterin the gel during vulcanization, as explained in the Beckmann patent,. being important to secure the microporous character of the rub- Kber during and after vulcanization.

It is important to the attainment of the desired 25 results, in makingl our improved composite diaf phragm, that a method be employed of such a nature that a controllable amount of latex oompound be causedb to gel on the two surfaces and in'the interstices of the fabric, and it is desirable 30 also that a method be employed such that-the diaphragms are produced by a continuous process, at least up to the point of vulcanization.

. 'I'hese results are obtained by the below described method, which, briefly stated, is:

Frst.-Impregnating the fabric, which can be of any desired predetermined width and either of predetermined or indefinite length, with the gelling solution which is preferably magnesium sulphate of a deiinite strength, depending upon the nature of the coating required.

Second-The volume of the gelling solution retained in the fabric is regulated to the desired amount, so as to remove the excess solution and leave the interstices open.

Third-The impregnated fabric is then passed through a rubber dispersion, such as a bath of latex compound of known solid content, preferably with the fabric stre I'ched taut, in a manner 50 and the process is preferably speeded by passing 55 the gelling: sheet through hot water vapor (exhaust steam, for example) so as to set the gel without loss of retained water. In so doing, the gel is iirmly set before it is allowed to touch anything which will 'disturb its structure, as

otherwise it will collapse, losing its porosityv vor separating from thefabric. After the gel is set, a continuous ilhn of dispersed rubber-water gel .covers the sides and fills the interstices of the fabric, so as to provide a condition which, after -vulcanization, forms an interlock between the coating which may have been caused by bubbles due to air trapped in the meshes of the fabric during impregnation. After the sheet is given two or more passes through the gelling solution and latex compound, it is preferably caused to travel through a chamber containng hot water vapor after each such pass in order to hasten the gelling and cause the gel to set.

Sixth-The gelled strip is then vulcanized Without permitting the escape of the retained Water, thus converting the set gel into microporous hard rubber. The vulcanization can be carried out in different ways, as will be explained subsequently.

In the drawing, I0 represents a diaphragm in the form of a separator adapted to be placedbetween the plates in a storage battery of the lead-acid type. The microporous rubber which coats the sides and fills the interstices of the fabric is indicated atA Ia', and thel fabric itself at Ilib. This separator is shown as provided with ribs Il which are' preferably vulcanized to the separator body during the vulcanizing operation referred to above.v ,'The ribs may be formed of different materials, such as hard rubber or strips cut ,n and third mentioned types of ribs possess consderable advantage over ribs of plain rubber in that the ribs themselves, being of a porous nature, do not increase the electrical resistance o f the separator to any appreciable extent. Furthermore, due to the' fact that these ribspare porous, the separatorsv as a whole do not displace as much electrolyte as would otherwise be the case.

We donot regard it essential that the ribs be formed `on 'the sheet by vulcani'zing rib-forming material thereon, as integral ribs may be provided by doubling portions of the sheet upon itself so as to make rib-forming folds. vWe might say, however, that we do not regard it essential that the separators be provided withribs of any kind for the equivalent of the same can be secured `by giving the sheet a corrugated form during vulcanization. The ribbed type is preferred by us, however, and further reference -to the ribbing will be made later.

One way of vulcanizing and applying the ribs is as follows: 'Ihe gelled strip may be cut into predetermined lengths and placed between mold plates, one ofwhich may be provided with grooves in which is placed the rib-forming material, such as strips formed from hard rubber composition or strips cut irom the gelled sheet treated in the manner just explained, or any other material which can be vulcanized to the strip during the vulcanizing operation. In practice', when a quantity of pairs of mold plates have had placed between them the pieces of the gelled strip and ribforming material, the mold plates are placed in a vulcanizer and vulcanized in steam (or under water) so that during vulcanization the water will be retained in the reticular structure of the gel and the latex will be vulcanized to hard rubber and will, after vulcanization, have the microporous condition already explained and more fully described in the Beckmann patent refered to.

Instead of proceeding as above described, the gelled strip may be wound upon a drum, and, at the same time, rib-forming material, preferably gelled rib-forming material, is laid on the strip and caused to adhere thereto. At the same time, a fabric liner may be wound on the drum so as to separate the different convolutions of the gelled strip and keep them from sticking together which liner may be grooved to receive the ribforming material. Next the loaded drum is conf. veyed to a vulcanizer where the gelled mass is vulcanized to hard rubber without the escape of the retained water. After vulcanization, the sheet or strip which is ribbed and is coated and has its interstices illled with microporous hard rubber is cut into sections of the size desired for storage battery separators.

separators composed wholly of microporous Vrubber or even with fabric covered with preboth sides of the porous material, such as openweave fabric. The two layers are not only interlocked or formed continuous through the fabric, but the layers on opposite sides can be made as thin as desired, such as in the form of thin coatings or films. y

Togive a specific instance of proportions, we might mention that very good results havebeen obtained with separators of this kind having a thickness 'of approximately .028 inch, using an open weave fabric having an average thickness of approximatelyv `.018 inch. In other words, the fabric thickness exceeds the combined thickness of the two layers or films on both sides of the fabric, which makes it apparent that separators made in accordance with this -invention and utilizing-an inner sheet of open weave fabric in and on whichthe gel is produced and later converted into microporous rubber requires only a relatively thin outside layer of this microporous rubber to give the separator the desired strength and stiiness, this being an important factor in the attainment ofthe desirable lowl electrical resstanceg, So far as we are aware, these satisfactory results, especially the absolute control of the thickness of the layers which are applied to the fabric sheet, cannot be obtained by any other process than the one herein explained which has for its important characteristic the fact that. the sheet is impregnated with a gelling solution and then passed through a latex or other dispersed rubber solution the concentration of which may be varied as desired, as can also the speed of passing the fabric through the bath, as well as the number of passes through the gelling solution and through the latex solution. Although the process is described and claimed in our Patent No. 2,052,490 referred to above, some of the important phases thereof are herein dwelt upon to emphasize the novel structural characteristics of the separator of this application andthe important advantages of those novel structural characteristics.

We aim in our claims to cover all modifications which do not involve a departure from the spirit and scope of the invention in its broader aspects.

f Having thus described our invention, we claim:

1. A porous diaphragm comprising a porous inner sheet having its interstices filled and its sides covered with thin films of vulcanized microporous rubber.

2. A porous diaphragm comprising a sheet of fabric having its side's covered with thin lms of vulcanized microporous rubber which extends through the openings of the fabric so as to interlock the two films.

3. A diaphragm consisting of a sheet of fabric having relatively thin layers of vulcanized micro# porous rubber covering both sides and extending into the interstices thereof.

4. A diaphragm composed of an inner layer of fabric covered with vulcanized microporous rubber for-med from rubber gel produced directly on the fabric and vulcanized while the liquid of the gelis interstitially included therein.

5. A diaphragm composed of an inner layer of fabric having its sides covered with vulcanized microporous rubber formed from rubber gel produced directly on the sides and in the interstices of the fabric and vulcanized while the liquid of the gel is interstitially included therein.

6. A diaphragm composed of an inner sheet of fabric covered with thin films of vulcanized mi-` therein.

WILLARD L. REINHARDT. LELAND E. WELLS. 

